Structure of plant cell wall and their functions

1. PLANT CELL WALL
STRUCTURE AND
FUNCTIONS
DR. DILIP V. HANDE
ASSOCIATE PROFESSOR, DEPT OF BOTANY
SHRI SHIVAJI SCIENCE COLLEGE, AMRAVATI MS.

2. CELL WALL – STRUCTURE AND FUNCTION
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3. CELL WALL
 The cell wall is perforated at one or more
places through which the cytoplasm of a
cell is connected with that of adjacent cells.
 These cytoplasmic bridges interconnecting
any two adjacent cells are termed as
pldsmodesmata.
 These are of great physiological
importance because they allow flow of
cytoplasmic materials from one cell to the
other.
 Between the walls of any two adjacent cells
intercellular substance is deposited in the

4. CELL WALL
 In plants the middle lamella is formed of
calcium pectate.
 The intercellular matrix cements the cells
together cell wall to cell wall or pellicle to
pellicle.
 The middle lamella and outer cell wall or
pellicles are emphasized as non-living
because of the fact that they do not play
important role in the life of cell.

5. CELL WALL
 The cell wall or pellicle can be removed
from a number of plant and animal cells by
microsurgery and other techniques.
 In plants the cell wall can be differentiated
into primary, secondary and sometimes
tertiary layers.
 The secondary layer is deposited on the
inner face of the primary membrane and
the tertiary layer below the secondary one.

6. CELL WALL
 Electron microscopy has revealed that the
primary cell wall is composed of sub-
microscopic strands of cellulose.
 which in turn can be split into even finer
threads by means of ultrasonic irradiations.
 These microfibrils of the primary wall layer
are interwoven to form a very dense network.

7. CELL WALL
 The microfibrils of cellulose in the secondary
cell wall tend to lie in parallel fashion forming
successive lamellae instead of forming a
network.
 In the successive layers of secondary wall
the orientation of the parallel microfibrils is
changed.

8. CELL WALL
 At certain places the microfibrils of
secondary wall materials are not
deposited, resulting thereby depressions
or perforations.
 Such characteristic perforations in the
secondary "walls are known as pits.
 There are micro capillary spaces between
the microfibrils of cellulose in the
secondary wall.

9. CELL WALL
 In these microcapillary spaces lignin, cutin,
suberine, hemicelluloses, minerals and
some other wall materials are deposited.
 which make the secondary wall tensile
and sometime impermeable to water and
gases .

10. CELL WALL
 In general, the structure and the chemical
constitution of cell walls will vary according
to the physiology of plant tissue in which
they are found.
 The cell wall provides rigidity and support
to the cells.
 It also protects the protoplasm from
mechanical injury and maintains the
characteristic shape of cell.

11. STRUCTURE:
 In plant cell wall is present outside the
plasma membrane of every cell.
 It is made up of dead matter secreted by the
protoplasm.
 Its structure and thickness varies in different
tissue of the plants.
 It is relatively thin in parenchymatous tissue
and is probably thickest in xylem vessels.

12. STRUCTURE:
 In plant cell wall is present outside the
plasma membrane of every cell.
 It is made up of dead matter secreted by the
protoplasm.
 Its structure and thickness varies in different
tissue of the plants.
 It is relatively thin in parenchymatous tissue
and is probably thickest in xylem vessels.

13. ULTRASTRUCTURE
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14. STRUCTURE
 The plant cell wall is differentiated into
following layers:
 Middle lamella
 It is the intracellular matrix between adjacent
cells and holds the cells of the tissue
together.
 It is always found between the primary cell
wall of neibouring cells.
 It is composed of pectates of calcium and
magnesium along with protein component.
 It can be dissolved by strong acids.

17. ULTRASTRUCTURE
 Primary cell wall
 It is the true cell
wall which
develops in the still
growing cells and
lies on the inner
side of the middle
lamella.
 It is formed of
pectates, cellulose,
hemicelluloses and
some
polysaccharides.

18. SECONDARY CELL WALL-
 It is found in the mature or non-growing cells.
 It is laid down on the inner side of the primary wall
and develops only in those cells which have
ceased to grow.
 It is thick and rigid and provides great tensile
strength to the cell.
 It is composed of three successive layers of
cellulose microfibrils in gelatinous matrix, formed
of hemicelluloses and other polysaccharides.
 In addition, it may be deposited with inorganic
salts, tannins, waxes, calcium salts, silica, lignin,
suberin and cutin etc.

19. ULTRASTRUCTURE
 When cell wall after
maceration, is studied
under the electron
microscope, it reveals
two main parts- the
matrix and fibril.
 The matrix-
 It is the ground
substance in which
fibrils are embedded. It
is amorphous and is
deposited with pectin,
lignin or
hemicelluloses.

20. ULTRASTRUCTURE
 The fibrils-
 The fibrils are composed
of cellulose. The
cellulose molecules are
polymer of disaccharide
cellobiose having approx.
3000 glucose unit which
are arranged in linear
order.
 The cellulose molecules
of the primary wall are
arranged along the
longitudinal axis of the
cells in definitely
organized longitudinal
bundles.
 These bundles are
known as macrofibrils.

21. ULTRASTRUCTURE
 The microfibrils are
about 100-150A in
diameter and about
1µ long.
 These are thread
like structures
called microfibrills.
 Each microfibrills is
composed of 20
micelles.
 Micelles are
composed of about
100 individual
cellulose chains.

22. FUNCTIONS
 The function of the plant cell wall:
1. Maintains cell shape.
2. Prevents the rupture of the cell when
excess water enters the cell by osmosis.
3. Filters out large molecules but allows
smaller proteins and nutrients to enter.
4. The plant cell wall is mostly made up of
cellulose, a linear polymer made up of
several hundred to ten thousand D-glucose
molecules chemically joined together.
5. As there is hydrogen bonding in between in
the glucose molecules in different strands,
this
makes the whole cell wall rigid and
inflexible.

23. FUNCTIONS
 6. Thus when excess water enters the cell
by osmosis, the cell expands and presses
on the cell wall. Since the cell wall is
inflexible, it exerts a force back on the cell.
 7. Allows plant cell to stay in hypotonic
solution (animal cells go through
hemolysis because they lack a cell wall)
8. Function as building material for plants

24. THANKS